1. Field of the Invention
The present invention generally relates to a method and apparatus for sensing a condition of a power supply, and more particularly to sensing a failure of an energy storage device such as an electrolytic capacitor or battery.
2. Description of the Related Art
Modern information technology equipment requires extremely reliable power supplies. These power supplies utilize large electrolytic capacitors as energy storage devices, which are rated for upwards of hundreds of microfarads at hundreds of volts. These power supplies are designed to operate the capacitor well within its margin, and are indicated to have a certain operating life. However, environmental and operating conditions could lead to the capacitor operating outside of its margins, resulting in a premature failure.
The conventional method of containing a capacitor failure is to create structurally weaker parts of the capacitor package, which allow the capacitor to vent (i.e., vent smoke) rather than explode. However, failure of these conventional capacitors still results in a non-functional power supply, coinciding with a smoke event and leakage of electrolyte.
These power supplies, or AC-DC converters, employ a boost topology that converts the AC input to high-voltage DC which is then converted into the desired DC output.
An electrolytic capacitor is a component that has a limited life span. As it deteriorates, the capacitor may experience one of several failure modes. Some of these failure modes result in heating of the electrolyte, which causes hydrogen gas to be formed, which in turn creates a buildup of pressure internal to the capacitor. When the pressure is too great to be contained within the capacitor, the package vents through its pressure relief structure to prevent an explosion. FIG. 1 illustrates a conventional capacitor 100. In FIG. 1, capacitor 100 includes capacitor walls 110 and vents 120. Thus, when pressure in capacitor 100 increases, vents 120 may open to allow relief of the pressure buildup.
The venting incident will release solvents into the environment such as ethylene glycol. These solvents are not toxic but can act as an irritant. Shutting down the power supply that contains a capacitor that is building up an internal pressure will prevent it from venting.
Modern information technology equipment and telecom equipment also make use of batteries as a back-up feature during loss of the AC utility or to enable portability. Abnormal operating conditions can lead to a buildup of internal pressure, causing the battery cell to rupture. This safety hazard is especially severe with Lithium-Ion batteries, which can cause a fire.
In addition, electrolytic capacitors are present in many power converter technologies. In these technologies, ripple currents can become very high and can lead to increased internal heating and shortening of the life of the capacitor.
Thus, a need exists to monitor and protect conventional power supplies, such as electrolytic capacitors and batteries.